Poor Man Profiler - knowing CPU usage

10 Jun 2014

We usually face a situation that we don’t know which parts in the program use more CPU time. Therefore, there are so many application profiler out there. For instance, Oprofile is a famous profiler, which could be used to monitor the application. Poor Man Profiler, however, could further provide the benefit of tracking the complete stack and profiling all threads of to the same process.

Using Poor Man Profiler does not have to install other packages, as long as you have GDB in your computer (so it is for *nix-system only). The core of the profiler only relies on one line of code:

gdb -ex "set pagination 0" -ex "thread apply all bt" -batch -p pid_of_your_program

Demonstration

To demonstrate its powerness, I worte a perl program in the below.

#!/usr/bin/env perl -w
#############################################################
# poor_man_profiler.pl                                      #
#############################################################

use strict;
use warnings;

my $proc_name = shift @ARGV;

$SIG{INT}  = \&signal_handler;

my $output_string = "";
my %output_agg;
my %lib_agg;


my $stop_flag = 0;

my $result;
my $item;

print "START profiling....press [Ctrl-C] to stop\n";

my $pid = `pidof $proc_name`;

while(!$stop_flag) {
	$result = `gdb -ex "set pagination 0" -ex "thread apply all bt" -batch -p $pid`;
	
	for (split /^/, $result) {
		if ($_ =~ /^Thread/) {
			if ($output_string ne "") {
				if (not exists $output_agg{$output_string}) {
					$output_agg{$output_string} = 1;
				} else {
					$output_agg{$output_string}++;
				}

				$output_string = "";
			}
		}
		
		if ($_ =~ /^\#/) {
			my @s_result = split(' ', $_);

			if ($output_string ne "") {
				$output_string = $output_string.", ";
			}
			
			if ($s_result[2] eq "in") {
				$output_string = $output_string.$s_result[3];
			} elsif ($s_result[3] eq "at") {
				$output_string = "[at]".$output_string.$s_result[1];
			}
			
			if ($s_result[@s_result-1] ne "()") {
				my $get_lib = (split /\//, (split /:/, $s_result[@s_result-1])[0])[-1];
				
				if (not exists $lib_agg{$get_lib}) {
					$lib_agg{$get_lib} = 1;
				} else {
					$lib_agg{$get_lib}++;
				}
			
			
				$output_string = $output_string."(".$get_lib.")";
			}
		}
	}
	
	if ($output_string ne "") {
		if (not exists $output_agg{$output_string}) {
			$output_agg{$output_string} = 1;
		} else {
			$output_agg{$output_string}++;
		}
	}

	sleep (1);
}

print "profiling STOP!!!\n";

print "==\n";
my $total_output_percentage = 0;
foreach $item (keys %output_agg) {
	$total_output_percentage += $output_agg{$item};
}

my $output_percentage;
print "   samples |  %  | stack path\n";
foreach $item (sort {$output_agg{$b} <=> $output_agg{$a}} keys %output_agg) {
	$output_percentage = $output_agg{$item}/$total_output_percentage*100;
	printf "%10d | %3d | %s\n", ($output_agg{$item}, $output_percentage, $item);
}

print "==\n";
my $total_lib_percentage = 0;
foreach $item (keys %lib_agg) {
	$total_lib_percentage += $lib_agg{$item};
}

my $lib_percentage;
print "   samples |  %  | model name\n";
foreach $item (sort {$lib_agg{$b} <=> $lib_agg{$a}} keys %lib_agg) {
	$lib_percentage = $lib_agg{$item}/$total_lib_percentage*100;
	printf "%10d | %3d | %s\n", ($lib_agg{$item}, $lib_percentage, $item);
}

exit;

sub signal_handler {
    $stop_flag = 1;
}

The usage of this command is:

$ perl poor_man_profiler.pl process_name

The example output is:

$ sudo perl poor_man_profiler.pl top
START profiling....press [Ctrl-C] to stop
^Cprofiling STOP!!!
==
   samples |  %  | stack path
        13 | 100 | __kernel_vsyscall, select(libc.so.6), ??, __libc_start_main(libc.so.6), ??
==
   samples |  %  | model name
        14 | 100 | libc.so.6

I use sudo to run my program because this program is not belong to me.